Tips and common mistakes

Low and slow is the basis of everything (pickup, water drop, loading). Watch AGL and speed.
Hot missions: don't sit on the ground — hoist/hover and get out, the QRF is coming.
With patients, fly smoothly (G-monitor) — abrupt flying kills them.
Firefighter: aim the water into the wind with lead, drop low.
Can't see the fire physically? That's an old-version bug (effect below terrain) — report it; new versions place it on the ground.
A full bucket / full helo = worse performance, account for it on takeoff and in turns.
Cooperate: in disasters and big fires more aircraft = an easier job.

Based on the pilot guide (mission BETA2.99.23). Post your questions and experience in this thread.